Producing olefins from methanol have been considered an interesting alternative to the traditional production of olefins from petroleum. Methanol is considered to be a readily stored and managed intermediate product for utilization of hitherto unused natural gas. Thus, the increasing demands for olefins on the world market could also be served by using very cheap methane. For this reason, processes are being developed that produce short-chain olefins from methanol. Such processes operate, for example, catalytically according to the overall equation 2CH3OH→C2H4+2H2O. Besides the desired olefins, ethylene and propylene, longer-chain olefins and, especially, undesired compounds of hydrocarbons with oxygen (oxygenates) such as alcohols, ketones and organic acids also form. For this reason a costly secondary purification of the reaction product is necessary. One oxygenate that is particularly to be taken into account is dimethyl ether (DME), since it is one of the lightest oxygenates and behaves similarly to C3 in distillation processes. Moreover, it is only slightly polar, so it can be difficult to remove by absorption. Accordingly, it would be beneficial to find additional methods to more easily remove oxygenates from olefins, particularly from an olefin stream synthesized from methanol
U.S. Pat. Nos. 4,547,602 and 4,560,537 disclose a process for converting methanol to heavy hydrocarbons in the distillate range. In the first stage catalytic process, oxygenate is converted to lower olefins. The first stage effluent is cooled in an exchanger to condense water and a major amount of C5+ hydrocarbons. Byproduct water may be recovered from unreacted feedstock and discarded or a portion may be recycled.
U.S. Pat. No. 4,387,263 discloses a process for making C2 to C4 olefins from gas mixtures containing methanol, dimethyl ether. The reaction gasses, after condensation directs the reaction gasses and a condensed aqueous phase to a water scrubber in a water scrubbing column.
European Patent Application No. 0 060 103 discloses a process for converting methanol and/or dimethyl ether to a product containing ethylene. The product is condensed to form three phases—a liquid aqueous phase, a gaseous hydrocarbon phase and a liquid hydrocarbon phase. The liquid aqueous phase contains unreacted methanol and dimethyl ether. The liquid aqueous phase is stripped with low pressure steam to volatilize the methanol and/or dimethyl ether to from the aqueous phase. The methanol and/or dimethyl ether are recycled back to the reactor. Additionally, the gaseous hydrocarbon phase is contacted with methanol to selectively sorb unreacted dimethyl ether. An alternative contacts the gaseous phase with water to selectively remove dimethyl ether.